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Wednesday, March 25, 2015
11:00 AM - 12:00 PM
CNLS Conference Room (TA-3, Bldg 1690)

Seminar

A curious case of two-dimensional aggregates: in sync spatio-temporal heterogeneities.

Tamoghna Das
Okinawa Institute for Science and Technology

Relation between microscopic structures and governing dynamics in non-equilibrium particulate systems are often unclear. Using molecular dynamics simulations, we study this relationship for the case of two-dimensional (2D) aggregates. The aggregates formed due to competing interactions show a hierarchy of morphologies and transition in microscopic dynamics accordingly. The specific model system chosen for this study is representative of globular proteins and polymer coated colloids. The observed phenomena should, however, hold for other aggregate forming systems. By tuning the competition between short-range attraction and long-range repulsion among particles, we observe a sequence of non-compact to compact to percolated morphologies at a fixed density and temperature. Encoding the details of interactions into a single dimensionless parameter, we have successfully marked the transition points in terms of configurational randomness in this sequence. This minimal description is experimentally accessible through a master relation between the second virial coefficient and the parameter mentioned. Following a slow cooling protocol to form these aggregates, which is in contrast to the usual fast quench protocol, we show the geometric transition inherent to the competing interaction is enough the set non-ergodicity in the system. While the microscopic dynamics is sub-diffusive for all morphologies, the details are dependent on the later. The particles in compact clusters show caging dynamics in contrast to the bonding scenario observed in non-compact ones. Finally, by following the temperature dependence of the dynamics, we present a generic relation between position randomness and average diffusivity for two-dimensional aggregates.

Host: Turab Lookman